Researchers at AIST, in collaboration with Kirin Holdings Co., Ltd., Tokyo University of Agriculture and Technology, and Kyoto University, have developed a technology that transitions microbial communities in fermentation industry wastewater treatment plants from the nitrogen-removal to -recovery type.
While nitrogen compounds are essential for our social activities, their environmental impact has become a concern. To mitigate this environmental impact, current treatment plants for industrial wastewater containing nitrogen compounds convert these compounds into nitrogen gas through biological reactions and subsequently release it into the atmosphere. However, this process consumes energy through aeration to supply large amounts of oxygen. If these microbial conversion reactions could be halted at the intermediate product, i.e., ammonium ion, and the ion could be recovered, it would not only reduce energy consumption but also make it possible to utilize the ammonium ion as an energy resource. To achieve this, it is necessary to control the nitrogen conversion function of the microbial communities in the activated sludge in the treatment plant. But research on the control conditions and the microbial community's response has not progressed sufficiently.
In this study, using scaled-down processes of actual treatment plants and simulated wastewater derived from real streams, we resolved a major bottleneck in acclimating activated sludge microbial communities from nitrogen-removal to nitrogen-recovery type by applying low dissolved oxygen (DO) and low pH conditions. Our developed technology, the "Microaerobic Activated Sludge process" enables the recovery of ammonia, which is generated from nitrogen compounds in wastewater, as an energy resource through the downstream separation and concentration technologies. These processes are expected to facilitate a shift in wastewater treatment from decomposition and removal to treatment that enables energy recovery without requiring major modifications to the existing treatment plants.
Background
Nitrogen compounds are essential fertilizers that support crop growth and food production. They are also used as raw materials for pharmaceuticals and chemical products. However, according to the "Planetary Boundaries" framework, emissions of nitrogen compounds resulting from human activities have exceeded the Earth's acceptable capacity, exposing us to extremely high risk. Excessive emissions of nitrogen compounds into the environment can lead to a range of adverse impacts, including the eutrophication of lakes and coastal waters, acid rain, and global warming driven by nitrous oxide emissions.
Organic wastewater from the fermentation industry that produces food and pharmaceuticals contains low concentrations of nitrogen compounds. Currently, in the activated sludge process for treating this wastewater, the nitrogen compounds are biologically converted into ammonium ions. These ions are then transformed to nitrite, nitrate, nitric oxide, nitrous oxide, and are finally released into the atmosphere as nitrogen gas (known as nitrification-denitrification treatment process). This process requires large amounts of oxygen, resulting in significant energy consumption due to aeration. To enable efficient conversion and recovery of low-concentration nitrogen compounds in wastewater as ammonium resources, controlling the microbial community functions in microaerobic activated sludge is crucial; however, such control technology has not yet been established.
Points
- Using a scaled-down process based on actual fermentation industry wastewater treatment plants and simulated wastewater generated from the production stream, we successfully demonstrated the acclimation of microbial community from a nitrogen-removal type to a nitrogen recovery-type.
- By optimizing a microaerobic activated sludge process, nitrogen compounds in the wastewater were converted into ammonium ions, which can be used as an energy resource. The process was also controlled to prevent additional biological nitrogen transformation reactions.
- This development supports the transition from current nitrogen-removal plants, which convert nitrogen compounds into nitrogen gas and release it into the atmosphere, to energy-recovery plants.
